This invention relates in general to lamp control, and more particularly to a system and method for controlling lamp operation, such as ultraviolet (UV) and fluorescent lamp operation, in brownout and other substandard source voltage conditions.
Increased consumer power, deregulation laws, and other factors have imposed additional physical and economic stresses on utility organizations, thereby threatening record occurrences of power line phase droop and interruption events characteristic of poor transmission line regulation. In some cases, it is estimated that power line transmission losses will triple for utility companies.
Low line voltage or xe2x80x9csagxe2x80x9d can have a significant impact on electrical equipment and products. For example, power supplies in some electronic equipment may fall out of regulation, motors can overheat or slow down, electrical interference may increase, etc. One product category that is significantly impacted by poor power line regulation includes ultraviolet/fluorescent lamps, that can flicker extensively under brownout conditions. In addition to the potentially undesirable visual effects, this flickering can damage the filaments of the lamp and cause premature lamp mortality. Lamps that would otherwise likely meet expected warranty periods or other commercial expectations can thus fail due to brownout conditions that are beyond the control of lamp manufacturers, product developers, and consumers.
Premature lamp mortality occurs in brownout or other low line voltage conditions as a result of the physics underlying ultraviolet (UV) lamp technology. In UV and fluorescent lamps, a sealed glass tube generally includes a small amount of mercury and an inert gas. The tube generally includes two electrodes or xe2x80x9cfilaments,xe2x80x9d one at each end of the tube, which are wired to an electrical circuit coupled to an alternating current (AC) power source. When the lamp is initially turned on, electricity heats up the filaments, which boils off electrons from the metal surface into the gas tube, which in turn ionizes the gas and creates an electrically conductive medium. At this point, the lamp""s ballast provides the voltage kick across the filaments to establish an electrical arc through the gas. The resulting collision of free electrons with atoms releases other electrons, which creates ions, and ultimately plasma which establishes a path for an electrical current. Electrons migrating through the tube provide energy that causes some of the mercury to change to a gaseous state, which collides with the electrons and charged atoms. These collisions excite the atoms and bumps the electrons to higher energy levels, and when the electrons return to their original level, light photons are released.
When AC power is diminished due to brownout or other low voltage conditions, enough voltage may still be provided to create the arc through the gas, but not enough voltage to sustain the arc and resulting current through the lamp. In such a case, arcing occurs repeatedly, which causes the flickering effect. When the lamp flickers in this manner, the filaments are continually called upon to boil off electrons from its metal surface to ionize the gas and establish the arc. This degenerates the integrity of the filament, and ultimately causes lamp failure. More particularly, when the lamp is subject to low line conditions, the operating lamp""s cathode glowing layers cover only part of the cathode. When this occurs, the glow moves around, causing the flickering effect. If the available current is enough to cause the cathode to be covered with glow, the voltage drop of the cathode will be higher than what is expected under normal operation, causing ions to bombard the cathode with increased force and accelerating the sputtering of cathode material atoms. This sputtering effect essentially xe2x80x9cevaporatesxe2x80x9d the cathode material, causing uneven discharge, and leaving the filament thinner in some areas. The weakened area of the filament becomes hotter, which leads to even faster evaporation, thereby causing the filament to burn back and the lamp to burn out. Some lamps may burn out the instant they are turned on, because a thinned filament in a cold state cannot withstand the inrush surge of energy.
UV lamps are commonly used in the context of fluorescent lighting, where the inside surface of the UV lamp is coated with a phosphor that gives off a white light when exposed to UV light. However, UV lamps are used in a wide variety of other contexts. For example, UV lamps can be used to kill airborne bacteria and surface mold in air treatment systems. One such UV air treatment system is available under the trade name xe2x80x9cEnviracaire Elite(trademark),xe2x80x9d provided by Honeywell Inc., Golden Valley, Minn., U.S.A. The lamp life of UV lamps used in these and other UV lamp applications can be significantly diminished as a result of brownouts and other low line voltage conditions.
Accordingly, there is a need for a system and method for increasing lamp life that otherwise could be degraded due to poor power line regulation. The present invention fulfills these and other needs, and offers other advantages over the prior art.
In accordance with one embodiment of the invention, a control system is provided for controlling operation of at least one lamp powered by a power source. The control system includes a monitor circuit to monitor at least one power characteristic of the power source, and to provide a signal indicative of the monitored power characteristic in response. A controller is coupled to the monitor circuit to receive the signal, and to interrupt power supplied by the power source to the lamp, when the signal indicates that a voltage of the power source is less than a voltage threshold.
In more particular embodiments of such a control system, the power characteristic being monitored may be the current through the lamp, which may become erratic under low voltage conditions. In this case, the monitor circuit includes a current monitor to monitor the current through the lamp, and to provide a signal indicative of the state of current flow through the lamp. The controller is coupled to the current monitor to receive this signal, and to interrupt power supplied by the power source to the lamp when the signal indicates an erratic state of current flow through the lamp as a result of the voltage being less than the voltage threshold.
In other particular embodiments of such a control system, the power characteristic being monitored may be the voltage itself provided by the power source. In this case, the monitor circuit includes a voltage monitor to monitor the voltage provided by the power source, and to provide a signal indicative of the voltage provided by the power source. The controller is coupled to the voltage monitor to receive this signal, and to interrupt power supplied by the power source when the signal indicates that the voltage is less than the voltage threshold. Any aspect of the voltage may be monitored, such as peak voltage, RMS voltage, etc.
In other particular embodiments of such a control system, a controllable switch is provided between the power source and the lamp. This controllable switch may be provided at any location between the power source and the lamp within the circuit path, such as on either the supply or return side of the lamp. Further, the controllable switch may be a discrete switch(s), or may be a switch associated with another component such as a ballast that includes an input(s) to control the ballast switch. In one embodiment of the invention, the controller interrupts power supplied by the power source to the lamp by automatically opening the controllable switch in response to the signal indicating that the voltage of the power source is less than the voltage threshold.
In still other particular embodiments of such a control system, the controller is further configured to restore power supplied by the power source to the lamp in response to at least one predetermined event. The predetermined event(s) may include, for example, an expiration of a predetermined time duration, an expiration of a predetermined count value, a time of day, a signal indicating acceptable source voltage levels, etc.
In accordance with another embodiment of the invention, an ultraviolet (UV) air treatment system for treating air provided by an air handling system is provided. The air handling system includes, for example, an air duct arrangement for channeling the air through a targeted space. The air treatment system includes at least one UV lamp positionable within the air duct arrangement. A controllable switch is coupled between a power source and the UV lamp to enable power to the UV lamp when the controllable switch is closed (i.e., allows current to flow), and to disable power to the UV lamp when the controllable switch is open (i.e., disables current flow). A monitor circuit monitors at least one power characteristic of the power source when the controllable switch is closed, and provides a signal indicative of the power characteristics in response. A controller is coupled to the monitor circuit to receive the signal, and to open the controllable switch when the signal indicates that a voltage of the power source is less than a voltage threshold.
In more particular embodiments of such an air treatment system, the power characteristic is a current, and the monitor circuit includes a current monitor to monitor the current through the UV lamp and to provide a signal indicative of a state of current flow through the UV lamp. The controller is coupled to the current monitor to receive the signal, and to interrupt power supplied by the power source to the UV lamp when the signal indicates an erratic state of current flow through the UV lamp resulting from the voltage being less than the voltage threshold.
In other particular embodiments of such an air treatment system, the power characteristic is a voltage, and the monitor circuit includes a voltage monitor to monitor the voltage provided by the power source, and to provide a signal indicative of the voltage provided by the power source. The controller is coupled to the voltage monitor to receive the signal, and to interrupt power supplied by the power source when the signal indicates that the voltage is less than the voltage threshold.
In accordance with another embodiment of the invention, a method is provided for controlling at least one lamp. The method includes monitoring an AC power characteristic of a power source supplying power to the lamp. A signal representative of a voltage level of the power source is generated, based on the monitored AC power characteristic. Connection of the power to the lamp is controlled based on the generated signal. In this manner, lamp operation may be controlled based on power characteristics of the power source.
In more particular embodiments of such a method, monitoring the AC power characteristic includes monitoring the AC voltage of the power source that supplies power to the lamp. In such a case, generating a signal representative of the voltage level of the power source includes generating a signal identifying the voltage level of the power source. In other particular embodiments of such a method, monitoring the AC power characteristic of the power source includes monitoring the AC current provided by the power source to the lamp. In such a case, generating a signal representative of the voltage level of the power source includes generating a signal corresponding to a current flowing through the lamp, which is dependent on the voltage level of the power source.
In other particular embodiments of such a method, controlling connection of the power to the lamp includes controlling a switch coupled in a circuit path that includes at least the power source and the lamp. Control of the switch is based on the generated signal representative of the voltage level of the power source. In other particular embodiments, controlling the switch involves opening the circuit path via the switch when the generated signal indicates that the AC power characteristic is not sufficient to maintain an uninterrupted current flow through the lamp, and may also involve closing the circuit path via the switch in response to at least one predetermined event.
In other particular embodiments of such a method, controlling connection of the power to the lamp involves performing at least one power interrupt cycle. Such a power interrupt cycle includes removing power and restoring power to the lamp. For example, power provided by the power source to the lamp may be removed using at least one switch circuit, when the generated signal indicates that the AC power characteristic is insufficient to maintain a stable current flow through the lamp. Power provided by the power source to the lamp may be restored using the switch circuit in response to at least one predetermined event. In various embodiments, the predetermined event(s) includes, for example, any one or more of expiration of a predetermined time duration, expiration of a predetermined count value, occurrence of a predetermined time of day, and occurrence of an indication that the AC power characteristic is sufficient to maintain a stable current flow through the lamp. In more particular embodiments, the number of power interrupt cycles that are occurring may be tracked, such that the current number of power cycle interrupts may be compared to a predetermined power interrupt cycle value. When the current number of power interrupt cycles reaches the predetermined power interrupt cycle value, the operation state may be changed. For example, different actions may take place depending on the current operation state. As a more particular example, one of the operation states may include a termination state where power interrupt cycles are terminated.
In other particular embodiments of such a method, the lamp(s) may be positioned in an air duct arrangement in an air treatment system. For example, the lamp may be an ultraviolet (UV) lamp used as a germicide in the air treatment system.